RFC 7650
A Constrained Application Protocol (CoAP) Usage for REsource LOcation And Discovery (RELOAD)
Pages: 19
Proposed Standard
Proposed Standard
Internet Engineering Task Force (IETF) J. Jimenez Request for Comments: 7650 Ericsson Category: Standards Track J. Lopez-Vega ISSN: 2070-1721 University of Granada J. Maenpaa G. Camarillo Ericsson September 2015 A Constrained Application Protocol (CoAP) Usage for REsource LOcation And Discovery (RELOAD)Abstract
This document defines a Constrained Application Protocol (CoAP) Usage for REsource LOcation And Discovery (RELOAD). The CoAP Usage provides the functionality to federate Wireless Sensor Networks (WSNs) in a peer-to-peer fashion. The CoAP Usage for RELOAD allows CoAP nodes to store resources in a RELOAD peer-to-peer overlay, provides a lookup service, and enables the use of RELOAD overlay as a cache for sensor data. This functionality is implemented in the RELOAD overlay itself, without the use of centralized servers. The RELOAD AppAttach method is used to establish a direct connection between nodes through which CoAP messages are exchanged. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7650.
Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Registering CoAP URIs . . . . . . . . . . . . . . . . . . . . 7 5. Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Forming a Direct Connection and Reading Data . . . . . . . . 9 7. Caching Mechanisms . . . . . . . . . . . . . . . . . . . . . 11 7.1. ProxyCache . . . . . . . . . . . . . . . . . . . . . . . 11 7.2. SensorCache . . . . . . . . . . . . . . . . . . . . . . . 13 8. CoAP Usage Kinds Definition . . . . . . . . . . . . . . . . . 14 8.1. CoAP-REGISTRATION Kind . . . . . . . . . . . . . . . . . 14 8.2. CoAP-CACHING Kind . . . . . . . . . . . . . . . . . . . . 15 9. Access Control Rules . . . . . . . . . . . . . . . . . . . . 15 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 11.1. CoAP-REGISTRATION Kind-ID . . . . . . . . . . . . . . . 17 11.2. CoAP-CACHING Kind-ID . . . . . . . . . . . . . . . . . . 17 11.3. Access Control Policies . . . . . . . . . . . . . . . . 17 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 12.1. Normative References . . . . . . . . . . . . . . . . . . 18 12.2. Informative References . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The Constrained Application Protocol (CoAP) Usage for REsource LOcation And Discovery (RELOAD) allows CoAP nodes to store resources in a RELOAD peer-to-peer overlay, provides a lookup service, and enables the use of RELOAD overlay as a cache for sensor data. This functionality is implemented in the RELOAD overlay itself, without the use of centralized servers. This usage is intended for interconnected devices over a wide-area geographical coverage, such as in cases where multiple Wireless Sensor Networks (WSNs) need to be federated over some wider-area network. These WSNs would interconnect by means of nodes that are equipped with long range modules (e.g., 2G, 3G, 4G) as well as short range ones (e.g., XBee, ZigBee, Bluetooth LE). Constrained devices are likely to be heterogeneous when it comes to their radio layer; however, we expect them to use a common application-layer protocol -- CoAP, which is a specialized web transfer protocol [RFC7252]. It realizes the Representational State Transfer (REST) architecture for the most constrained nodes, such as sensors and actuators. CoAP can be used not only between nodes on the same constrained network but also between constrained nodes and nodes on the Internet. The latter is possible since CoAP can be translated to Hypertext Transfer Protocol (HTTP) for integration with the web. Application areas of CoAP include different forms of machine-to-machine (M2M) communication, such as home automation, construction, health care or transportation. Areas with heavy use of sensor and actuator devices that monitor and interact with the surrounding environment. As specified in [RFC6940], RELOAD is fundamentally an overlay network. It provides a layered architecture with pluggable application layers that can use the underlaying forwarding, storage, and lookup functionalities. Figure 1 illustrates where the CoAP Usage is placed within the RELOAD architecture.
Application +-------+ | CoAP | ... | Usage | +-------+ ------------------------------------ Messaging Service +------------------+ +---------+ | Message |<--->| Storage | | Transport | +---------+ +------------------+ ^ ^ ^ | | v v | +-------------------+ | | Topology | | | Plug-in | | +-------------------+ | ^ v v +------------------+ | Forwarding & | | Link Management | +------------------+ ------------------------------------ Overlay Link Service +-------+ +-------+ |TLS | |DTLS | ... |Overlay| |Overlay| |Link | |Link | +-------+ +-------+ Figure 1: Architecture The CoAP Usage involves three basic functions: Registration: CoAP nodes that can use the RELOAD data storage functionality, can store a mapping from their CoAP URI to their Node- ID in the overlay. They can also retrieve the Node-IDs of other nodes. Nodes that are not RELOAD aware can use other mechanisms, for example [CORERESDIR] in their local network. Lookup: Once a CoAP node has identified the Node-ID for an URI it wishes to retrieve, it can use the RELOAD message routing system to set up a connection that can be used to exchange CoAP messages. Similarly as with the registration, nodes that are not RELOAD aware can use CoAP messages with a RELOAD Node (RN) that will in turn perform the lookup in the overlay.
Caching: Nodes can use the RELOAD overlay as a caching mechanism for information about what CoAP resources are available on the node. This is especially useful for power-constrained nodes that can make their data available in the cache provided by the overlay while in sleep mode. For instance, a CoAP proxy (See Section 3) could register its Node-ID (e.g. "9996172") and a list of sensors (e.g. "/sensors/temp-1; /sensors/temp-2; /sensors/light, /sensors/humidity") under its URI (e.g. "coap://overlay-1.com/proxy-1/"). When a node wants to discover the values associated with that URI, it queries the overlay for "coap://overlay-1.com/proxy-1/" and gets back the Node-ID of the proxy and the list of its associated sensors. The requesting node can then use the RELOAD overlay to establish a direct connection with the proxy and to read sensor values. Moreover, the CoAP proxy can store the sensor information in the overlay. In this way, information can be retrieved directly from the overlay without performing a direct connection to the storing proxy.2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. We use the terminology and definitions from the RELOAD Base Protocol [RFC6940] extensively in this document. Some of those concepts are further described in the "Concepts and Terminology for Peer to Peer SIP" [P2PSIP] document.3. Architecture
In our architecture we extend the different nodes present in RELOAD (Peer, Client) and add support for sensor devices or other constrained devices. Figure 2 illustrates the overlay topology. The different nodes, according to their functionality, are: Client As specified in [RFC6940], clients are nodes that do not have routing or storage responsibilities in the Overlay. Peer As specified in [RFC6940], peers are nodes in the overlay that can route messages for nodes other than those to which it is directly connected.
Sensor
Devices capable of measuring a physical quantity. Sensors usually
acquire quantifiable information about their surrounding
environment such as: temperature, humidity, electric current,
moisture, radiation, and so on.
Actuator
Devices capable of interacting and affecting their environment
such as: electrical motors, pneumatic actuators, electric
switches, and so on.
Proxy Node
Devices having sufficient resources to run RELOAD either as client
or peer. These devices are located at the edge of the sensor
network and, in case of Wireless Sensor Networks (WSN), act as
coordinators of the network.
Physical devices can have one or several of the previous functional
roles. According to the functionalities that are present in each of
the nodes, they can be:
Constrained Node
A Constrained Node (CN) is a node with limited computational
capabilities. CN devices belong to classes of at least C1 and C2
devices as defined in [RFC7228], their main constraint being the
implementation of the CoAP protocol. If the CN is wireless, then
it will be part of a Low-Rate Wireless Personal Area Network
(LR-WPAN), also termed Low-Power and Lossy Network (LLN). Lastly,
devices will usually be in sleep mode in order to prevent battery
drain, and will not communicate during those periods. A CN is NOT
part of the RELOAD overlay, therefore it cannot act as a client,
peer, nor proxy. A CN is always either a Sensor or an Actuator.
In the latter case, the node is often connected to a continuous
energy power supply.
RELOAD Node
A RELOAD Node (RN) MUST implement the client functionality in the
Overlay. Additionally, the node will often be a full RELOAD peer.
An RN may also be sensor or actuator since it can have those
devices connected to it.
Proxy Node
A Proxy Node (PN) MUST implement the RN functionality and act as a
sink for the LR-WPAN network. The PN connects the short range
Wireless Network to the Wide Area Network or the Internet. A
Proxy Node fulfills the "Proxy Node" role as described previously
in the Architecture.
+------+ | | +--------+ RN +---------+ | | | | +---+--+ +------+ +--+---+ | | | | | RN | | RN | | | | | +------------+ +---+--+ +--+---+ | WSN | | RELOAD | | +----+ | | OVERLAY | | +---+ CN | | +---+--+ +--+---+ | | +----+ | | | | +-----+ | | RN | | PN | | | | | | +-----+ | +---+--+ +------+ +--+---+ | | +----+ | | | | | | +---+ CN | | +--------+ PN +---------+ | +----+ | | | +------------+ +-+--+-+ | | +--------|--|--------+ | +--+ +--+ | | | | | | +--+-+ +-+--+ | | | CN | | CN | | | +----+ +----+ | | WSN | +--------------------+ Figure 2: Overlay Topology4. Registering CoAP URIs
CoAP URIs are typically resolved using a DNS. When CoAP is needed in a RELOAD environment, URI resolution is provided by the overlay as a whole. Instead of registering a URI, a peer stores a CoAPRegistration structure under a hash of its own URI. This uses the CoAP REGISTRATION Kind-ID, which is formally defined in Section 8.1 and uses a DICTIONARY data model. In this example, a CoAP proxy that is located in an overlay overlay-1.com using a Node-ID "9996172" wants to register four different sensors to the URI "coap://overlay-1.com/proxy-1/.well- known/". We will be using the link format specified in [RFC6690] to store the following mapping in the overlay:
Resource-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
KEY = 9996172,
VALUE = [
</sensors/temp-1>;rt="temperature-c";if="sensor",
</sensors/temp-2>;rt="temperature-c";if="sensor",
</sensors/light>;rt="light-lux";if="sensor",
</sensors/humidity>;rt="humidity-p";if="sensor"
]
Note that the Resource-ID stored in the overlay is calculated as hash
over the URI, that is -- h(URI), which in RELOAD is usually SHA-1.
This would inform any other node performing a lookup for the previous
URI "coap://overlay-1.com/proxy-1/.well-known" that the Node-ID value
for proxy-1 is "9996172". In addition, this mapping provides
relevant information as to the number of sensors (CNs) and the URI
path to connect to them using CoAP.
5. Lookup
The RELOAD overlay supports a rendezvous system that can be used for
the lookup of other CoAP nodes. This is done by fetching mapping
information between CoAP URIs and Node-IDs.
As an example, if a node RN located in the overlay overlay-1.com
wishes to read which resources are served at an RN with URI
coap://overlay-1.com/proxy-1/, it performs a fetch in the overlay.
The Resource-ID used in this fetch is a SHA-1 hash over the URI
"coap://overlay-1.com/proxy-1/.well-known/".
After this fetch request, the overlay will return the following
result:
Resource-ID = h(coap://overlay-1.com/proxy-1/.well-known/)
KEY = 9996172,
VALUE = [
</sensors/temp-1>;rt="temperature-c";if="sensor",
</sensors/temp-2>;rt="temperature-c";if="sensor",
</sensors/light>;rt="light-lux";if="sensor",
</sensors/humidity>;rt="humidity-p";if="sensor"
]
The obtained KEY is the Node-ID of the RN responsible of this KEY/
VALUE pair. The VALUE is the set of URIs necessary to read data from
the CNs associated with the RN.
Using the RELOAD DICTIONARY model allows for multiple nodes to
perform a store to the same Resource-ID. This can be used, for
example, to perform a store of resources of the same type or with
similar characteristics. After performing a lookup, this feature
allows the fetching of those multiple RNs that host CNs of the same
class.
As an example, provided that the previous peer (9996172) and another
peer (9996173) have stored the links to their respective temperature
resources in this same Resource-ID (temperature), an RN (e.g.,
node-A) can do a fetch to the URI "coap://overlay-1.com/
temperature/.well-known/", obtaining the following results:
Resource-ID = h(coap://overlay-1.com/temperature/.well-known/)
KEY = 9996172,
VALUE = [
</sensors/temp-1>;rt="temperature-c";if="sensor",
</sensors/temp-2>;rt="temperature-c";if="sensor",
]
KEY = 9996173,
VALUE = [
</sensors/temp-a>;rt="temperature-c";if="sensor",
</sensors/temp-b>;rt="temperature-c";if="sensor"
]
6. Forming a Direct Connection and Reading Data
Once an RN (e.g., node-A) has obtained the lookup information for a
node in the overlay (e.g., proxy-1), it can directly connect to that
node. This is performed by sending an AppAttach request to the
Node-ID obtained during the lookup process.
After the AppAttach negotiation, node-A can access the values of the
CNs at proxy-1 using the information obtained during the lookup.
Following the example in Section 5, and according to [RFC6690], the
requests for accessing the CNs at proxy-1 would be:
REQ: GET /sensors/temp-1
REQ: GET /sensors/temp-2
Figure 3 shows a sample of a node reading temperature data. +-----+ +---------+ +-----+ +---+ | PNA | | OVERLAY | | PNB | |CNB| +-----+ +---------+ +-----+ +---+ | | | | | | | | | 1.RELOAD | | | | FetchReq | | | |+----------->| | | | | | | | 2.RELOAD | | | | FetchAns | | | |<-----------+| | | | | | | | 3.RELOAD | | | | AppAttach | | | |+----------->| | | | | 4.RELOAD | | | | AppAttach | | | |+---------->| | | | | | | | 5.RELOAD | | | 6.RELOAD |AppAttachAns| | |AppAttachAns |<----------+| | |<-----------+| | | | | | | | | | | --------------------- | | | / 7.ICE \| | | \ connectivity checks /| | | --------------------- | | | | | | 8.CoAP CON | | | GET /sensors/temp-1 | | |+------------------------>| | | | 9.CoAP GET | | |/sensors/temp-1 | | |+-------------->| | | 10.CoAP | | 11.CoAP | ACK 200 | | ACK 200 |<--------------+| |<------------------------+| | | | | Figure 3: An Example of a Message Sequence
7. Caching Mechanisms
The CoAP protocol itself supports the caching of sensor information in order to reduce the response time and network bandwidth consumption of future, equivalent requests. CoAP caching is specified in Section 5 of [RFC7252]. It consists of reusing stored responses when new requests arrive. This type of storage is done in CoAP proxies. This CoAP usage for RELOAD proposes an additional caching mechanism for storing sensor information directly in the overlay. In order to do so, it is necessary to define how the data should be stored. Such caching mechanism is primarily intended for CNs with sensor capabilities, not for RN sensors. This is due to the battery constraints of CNs, forcing them to stay in sleep mode for long periods of time. Whenever a CN wakes up, it sends the most recent data from its sensors to its proxy (PN), which stores the data in the overlay using a RELOAD StoredData structure defined in Section 6 of [RFC6940]. We use the StoredDataValue structure defined in Section 6.2 of [RFC6940], in particular we use the SingleValue format type to store the cached values in the overlay. From that structure length, storage_time, lifetime and Signature are used in the same way. The only difference is DataValue, which in our case can be either a ProxyCache or a SensorCache: enum { reserved (0), proxy_cache(1), sensor_cache(2), (255) } CoAPCachingType; struct { CoAPCachingType coap_caching_type; select(coap_caching_type) { case proxy_cache: ProxyCache proxy_cache_entry; case sensor_cache: SensorCache sensor_cache_entry; /* extensions */ } } CoAPCaching;7.1. ProxyCache
ProxyCache is meant to store values and sensor information (e.g., inactivity time) for all the sensors associated with a certain proxy, as well as their CoAP URIs. SensorCache, on the other hand, is used for storing the information and cached value of only one sensor (CoAP URI is not necessary, as it is the same as the one used for generating the Resource-ID associated to that SensorCache entry).
ProxyCache contains the Node-ID, length, and a series of SensorEntry
types.
struct {
Node-ID Node_ID;
uint32 length;
SensorEntry sensors[count];
} ProxyCache;
Node-ID
The Node-ID of the Proxy Node (PN) responsible for different
sensor devices;
length
The length of the rest of the structure;
Sensor-Entry
List of sensors in the form of SensorEntry types;
SensorEntry contains the coap_uri, sensor_info, and a series of
SensorValue types.
struct {
opaque coap_uri;
SensorInfo sensor_info;
uint32 length;
SensorValue sensor_value[count];
} SensorEntry;
coap_uri
CoAP name of the sensor device in question;
sensor_info
contains relevant sensor information;
length
The length of the rest of the structure;
sensor_value
contains a list of values stored by the sensor;
7.2. SensorCache
SensorCache: contains the information related to one sensor. struct { Node-ID Node_ID; SensorInfo sensor_info; uint32 length; SensorValue sensor_value[count]; } SensorCache; Node_ID identifies the Node-ID of the Proxy Node responsible for the sensor; sensor_info contains relevant sensor information; length The length of the rest of the structure; sensor_value contains a list of values stored by the sensor; SensorInfo contains relevant sensor information that is dependent on the use case. As an example, we use the sensor manufacturer as relevant information. struct { opaque dev_info; /* extensions */ } SensorInfo; dev_info Contains specific device information as defined in [RFC6690] -- for example, temperature, luminosity, etc. It can also represent other semantic information about the device. SensorValue contains the measurement_time, lifetime, and value of the measurement.
struct {
uint32 measurement_time;
uint32 lifetime;
opaque value;
/* extensions */
} SensorValue;
measurement_time
indicates the moment when the measure was taken, represented as
the number of milliseconds elapsed since midnight Jan 1, 1970 UTC
not counting leap seconds.
lifetime
indicates the validity time of that measured value in milliseconds
since measurement_time.
value
indicates the actual value measured. It can be of different types
(integer, long, string); therefore, opaque has been used.
8. CoAP Usage Kinds Definition
This section defines the CoAP-REGISTRATION and CoAP-CACHING Kinds.
8.1. CoAP-REGISTRATION Kind
Kind-IDs
The Resource Name for the CoAP-REGISTRATION Kind-ID is the CoAP
URI. The data stored is a CoAPRegistration, which contains a set
of CoAP URIs.
Data Model
The data model for the CoAP-REGISTRATION Kind-ID is dictionary.
The dictionary key is the Node-ID of the storing RN. This allows
each RN to store a single mapping.
Access Control
URI-NODE-MATCH. The "coap:" prefix needs to be removed from the
COAP URI before matching.
Data stored under the COAP-REGISTRATION Kind is of type
CoAPRegistration, defined below.
struct {
Node-ID Node_ID;
uint16 coap_uris_length;
opaque coap_uris (0..2^16-1);
} CoAPRegistration;
8.2. CoAP-CACHING Kind
Kind-IDs
The Resource Name for the CoAP-CACHING Kind-ID is the CoAP URI.
The data stored is a CoAPCaching, which contains a cached value.
Data Model
The data model for the CoAP-CACHING Kind-ID is single value.
Access Control
URI-MATCH. The "coap:" prefix needs to be removed from the COAP
URI before matching.
Data stored under the CoAP-CACHING Kind is of type CoAPCaching,
defined in Section 7.
9. Access Control Rules
As specified in RELOAD Base [RFC6940], every Kind that is storable in
an overlay must be associated with an access control policy. This
policy defines whether a request from a given node to operate on a
given value should succeed or fail. Usages can define any access
control rules they choose, including publicly writable values.
CoAP Usage for RELOAD requires an access control policy that allows
multiple nodes in the overlay read and write access. This access is
for registering and caching information using CoAP URIs as
identifiers. Therefore, none of the access control policies
specified in RELOAD Base [RFC6940] are sufficient.
This document defines two access control policies, called URI-MATCH
and URI-NODE-MATCH. In the URI-MATCH policy, a given value MUST be
written and overwritten if and only if the signer's certificate
contains an uniformResourceIdentifier entry in the subjectAltName
Extension [RFC5280] that in canonicalized form hashes to the
Resource-ID for the resource. As explained in Section 6.3 of
[RFC7252] the "coap" and "coaps" schemes conform to the generic URI,
thus they are normalized in the generic form as explained in
Section 6 of [RFC3986]. The hash function used is specified in Section 10.2 of [RFC6940]. The certificate can be generated as specified in Section 9 of [RFC7252], using Certificate mode. In the URI-NODE-MATCH policy, a given value MUST be written and overwritten if and only if the condition for URI-MATCH is met and, in addition, the dictionary key is equal to the Node-ID in the certificate and that Node-ID is the one indicated in the SignerIdentity value cert_hash. These Access Control Policies are specified for IANA in Section 11.3.10. Security Considerations
The security considerations of RELOAD [RFC6940] and CoAP [RFC7252] apply to this specification. RELOAD's security model is based on public key certificates, which are used for signing messages and stored objects. At the connection level, RELOAD can use either TLS or DTLS. In the case of CoAP, several security modes have been defined. Implementations of this specification MUST follow all the security-related rules specified in the RELOAD [RFC6940] and CoAP [RFC7252] specifications. Additionally, in RELOAD every Kind that is storable in an overlay must be associated with an access control policy. This document specifies two new access control policies, which are specified in Section 9. These policies cover the most typical deployment scenarios. During the phase of registration and lookup, security considerations relevant to RELOAD apply. A CoAP node that advertises its existence via this mechanism, is more likely to be attacked, compared to a node (especially a sleepy node) that does not advertise its existence. Section 11 of [RFC7252] and Section 13 of [RFC6940] have more information about the kinds of attack and mitigation possible. The caching mechanism specified in this document is additional to the caching already done in CoAP. Access control is handled by the RELOAD overlay, where the peer storing the data is responsible for validating the signature on the data being stored.
11. IANA Considerations
11.1. CoAP-REGISTRATION Kind-ID
This document introduces a data Kind-ID to the "RELOAD Data Kind-ID" registry: +-------------------+------------+----------+ | Kind | Kind-ID | RFC | +-------------------+------------+----------+ | CoAP-REGISTRATION | 0x105 | RFC 7650 | +-------------------+------------+----------+ This Kind-ID was defined in Section 8.1.11.2. CoAP-CACHING Kind-ID
This document introduces another data Kind-ID to the "RELOAD Data Kind-ID" registry: +--------------+------------+----------+ | Kind | Kind-ID | RFC | +--------------+------------+----------+ | CoAP-CACHING | 0x106 | RFC 7650 | +--------------+------------+----------+ This Kind-ID was defined in Section 8.2.11.3. Access Control Policies
IANA has created a "CoAP Usage for RELOAD Access Control Policy" registry. This registry has been added to the existing RELOAD registry. Entries in this registry are strings denoting access control policies, as described in Section 9. New entries in this registry are to be registered per the Specification Required policy in [RFC5226]. The initial contents of this registry are: +-----------------+----------+ | Access Policy | RFC | +-----------------+----------+ | URI-NODE-MATCH | RFC 7650 | | URI-MATCH | RFC 7650 | +-----------------+----------+ This access control policy was described in Section 9.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, <http://www.rfc-editor.org/info/rfc3986>. [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, <http://www.rfc-editor.org/info/rfc5280>. [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, <http://www.rfc-editor.org/info/rfc6690>. [RFC6940] Jennings, C., Lowekamp, B., Ed., Rescorla, E., Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base Protocol", RFC 6940, DOI 10.17487/RFC6940, January 2014, <http://www.rfc-editor.org/info/rfc6940>. [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, <http://www.rfc-editor.org/info/rfc7252>.12.2. Informative References
[CORERESDIR] Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE Resource Directory", Work in Progress, draft-ietf-core- resource-directory-04, July 2015. [P2PSIP] Bryan, D., Matthews, P., Shim, E., Willis, D., and S. Dawkins, "Concepts and Terminology for Peer to Peer SIP", Work in Progress, draft-ietf-p2psip-concepts-07, May 2015.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>. [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, <http://www.rfc-editor.org/info/rfc7228>.Authors' Addresses
Jaime Jimenez Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: jaime.jimenez@ericsson.com Jose M. Lopez-Vega University of Granada CITIC UGR Periodista Rafael Gomez Montero 2 Granada 18071 Spain Email: jmlvega@ugr.es Jouni Maenpaa Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: jouni.maenpaa@ericsson.com Gonzalo Camarillo Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: gonzalo.camarillo@ericsson.com